Almost all water supply systems require metering devices to measure accurately, the amount of water utilized by a private customer or by a public facility. Special metering devices and associated accessories are required where the rate of such water utilization on occasion is particularly high, and the attendant supply lines must therefore be of large diameter. For example, the 4" to 10" water supply mains required for fire service lines have the capability of providing maximum water flow rates varying from 1000 to 5500 gallons per minute. These same lines, however, may also be used to provide domestic water, at a much lower usage rate, on a daily basis.
By way of example, in a hotel or a hospital, a single large line would be called upon to supply water to faucets, toilets and showers for regular daily use, and would also be relied upon to supply water to an automatic sprinkler system during an emergency. A satisfactory metering device for such dual purpose water service lines must be capable of measuring not only the maximum flow rates which might be encountered, but also low and intermediate flow rates as well.
Two-stage metering systems have been designed to measure both low and high flow rates through these dual purpose water supply lines. Typically, a large turbine meter is provided in the main line, having a high degree of accuracy from 20 to 50 gallons per minute, or so, up to the maximum flow rate for the line. Lower flow rates, down to 1 gpm, are accurately measured through a bypass piping system having a smaller 1" or 2" meter, known in the trade as a bypass meter. The bypass system is connected in parallel with the turbine meter, having a diversion connection upstream from the turbine meter, and a re-entry connection downstream from a spring loaded check valve, or crossover valve.
When water is flowing at a rate below approximately 20 gpm, it is diverted into the bypass line by the closed crossover valve, and the bypass meter measures water usage. Once the water flow exceeds the predetermined rate, the crossover valve is forced open, and the main turbine meter becomes operative along with the bypass meter.
The large mains and high volumes of water associated with a dual purpose water service line, or a dedicated fire service line, will readily pass debris, such as sand, small rocks, and pipe corrosion directly into operative parts of the main turbine meter. Thus, an accessory strainer is typically provided upstream from the turbine meter to catch and collect the debris, preventing it from damaging or destroying the turbine impeller.
A strainer designed for high volume, or fire service line applications must have the capacity to retain a large amount of captured debris. This is usually accomplished by providing a screened basket or a screened tube in the strainer housing, to intercept and capture the debris within the screen element. These strainers are known in the trade as basket strainers, "Y"-type strainers, and "in-line" strainers.
To meet current industry standards, a strainer must also display a low pressure loss, less than 3 psi, even when fouled with debris. To attain this objective, a ratio of 4 to 1 between the open screen area of the strainer and the cross-sectional area of the main line, is desired.
Older fire service line metering assemblies were simply a collection of the discrete meter, strainer, and check valve components, bolted together through the use of mating flanges and couplers. This resulted in an assembly that was physically large and heavy, as well as expensive to install and maintain.
More recently, manufacturers have combined certain of these previously separate components into the same body or housing. For example, a turbine meter has been combined with a downstream crossover valve by means of a common housing for both components. Similarly, the prior art shows a strainer and turbine meter combination, physically removed from each other, but mounted within a common casting. However, other than using a common housing for individual components, the known prior art has not structurally and functionally integrated the three main components of a high volume water line metering assembly, in the manner disclosed herein.